Sources: Luther, 95 Theses (1517); Luther, Freedom of a Christian (1520); Luther, Large and Small Catechisms (1529); the Augsburg Confession (1530, Melanchthon); the Formula of Concord (1577).

Lutheranism is the first and largest Protestant denomination, emerging from Martin Luther’s break with Rome in 1517–1521. Luther’s four core reforms: (1) Sola fide — justification (right standing before God) is received through faith alone, not supplemented by meritorious works; the breakthrough insight from Romans 1:17 (“the righteousness of God is revealed from faith to faith”); (2) Sola scriptura — Scripture alone is the supreme authority for doctrine; tradition and councils are subordinate and fallible; (3) Sola gratia — salvation is entirely by God’s grace; the human will is bound (De Servo Arbitrio, 1525 — against Erasmus’s defense of free will); (4) The priesthood of all believers — every Christian has direct access to God; the clergy are functionally distinct but not ontologically different. Lutheran sacramental theology: real presence in the Eucharist (“This is my body” taken literally — consubstantiation, not transubstantiation); infant baptism retained. The Lutheran territorial church model (cuius regio, eius religio — whose realm, his religion) settled by the Peace of Augsburg (1555). Today Lutheranism has ~75 million adherents, strongest in Germany, Scandinavia, and parts of Africa; the ELCA (USA), Church of Sweden, and German Evangelical Church are among the largest bodies.